HURRICANE AGNES and the GENESEE RIVER
FLOODING

The most destructive, widespread flooding to occur in the eastern United States occurred in June
1972 as a result of Hurricane Agnes. Unlike some other flood producing hurricanes in the
northeast, Agnes was not a particularly strong hurricane. In fact, most of its devastation occurred
well after it had been downgraded to a tropical storm. Agnes originated in the Gulf of Mexico
and slowly moved up the east coast before moving northwest across Pennsylvania and the
southern tier of New York state. At this point, the remnants of Agnes joined another large low
pressure system and continued to produce heavy rains.

The most significant destruction caused by Agnes, occurred in the Susquehanna River basin in
Pennsylvania. This is well documented by the NWS Middle Atlantic River Forecast Center.
This description will focus instead on the impacts on the Genesee River basin in western New
York.

During the week prior to Agnes, a large amount of shower activity resulted in widespread areas
of over an inch of rain. Heavy rain from Agnes started on the night of June 20 and continued until the 25th of June. Over
the Genesee River basin, the maximum official rainfall amount recorded was 13.7 inches at
Wellsville NY. Unofficial reports of over 16 inches were also received.

On the upper Genesee, above Mt Morris Dam, flooding was devestating breaking all historical
records. Both of the official river stage gages -- at Scio and Wellsville -- were destroyed by the
flooding. Hundreds of roads and bridges were washed out by the flood waters. One significant
factor in the damage was the large amount of debris flow that moved downstream which caused
significant scour and damming along various parts of the stream channel. The Wellsville area
was the hardest hit in the Genesee basin as a portion of Jones Memorial Hospital was destroyed
by the flood.

The lower Genesee mainstem, from Mt Morris to Rochester, was spared the worst of the flooding
primarily due to the operations of the dam. During the early part of the event, there was
significant concern of overtopping the spillway or having to release such major amounts of water
as to cause major downstream flooding. Overtopping would have been catastrophic in terms of
flow, but also would have allowed significant debris that was caught by the dam to be released
downstream. However, close monitoring and careful releases resulted in flooding downstream
but not nearly to the impact that could have occurred. Maximum inflow to the reservoir was
about 90,000 cfs; however, the outflow was limited to just over 15,000 cfs. While downstream
damage did occur, the Corps of Engineers estimated that the dam operations during Agnes alone
prevented over $200 million of additional potential damage.

Downstream flooding was also contributed to by tributaries, such as the Canaseraga Creek.
Downstream of Dansville, flood levees were overtopped. The levees, which were designed to
protect agricultural land, wound up causing problems since it took nearly all summer to drain the
fields following the flooding.